Description Of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
The present invention relates to a colour display device with backlighting unit using organic light-emitting diodes and also to a method of implementation of the said display device. It has applications in the field of electrically or electronically controlled displays in which a light beam or light beams produced by one or more light sources is/are optically switched by pixels in order to control the display of the light. It can more particularly be applied to liquid crystal displays (LCD) or displays using optical switching by micro-actuators (MEMS).
Displays implementing electro-optical switching arrays (or electro-optical modulators, these terms being equivalent), notably liquid crystal displays (LCD), are undergoing a significant development. In order to allow them to be used whatever the ambiant lighting conditions, a light source is required on which the electro-optical switching array can act. For this reason, in the case of colour LCD displays, it has been proposed to illuminate the LCD switching array from the rear (with respect to an observer situated in front of the display) with one or more cold cathode lighting tubes. Aside from the fact that their implementation is complicated, owing to the high voltage needed for their operation, and to the necessity of having a uniform distribution of light, they are fragile, have a limited lifetime (their characteristics degrade over time) and are power-hungry. In addition, since they produce white light, additional optical filtering devices are required in order to reproduce the whole of the visible colour spectrum on the display.
Other techniques for producing a backlighting have therefore been sought. Accordingly, after using light-emitting diodes, the implementation of organic light-emitting diodes (OLED) has been proposed. The latter technology, which allows three base spectral colours, red, green and blue (RGB), to be individually produced, and which, contrary to technologies of the cold cathode tube type, can be directly implemented at the rear of the LCD electro-optical switching array, allows the design of such displays to be simplified.
However, this technology still suffers from some limitations. Indeed, in known backlighting devices using OLEDs, the three RGB light sources are superimposed (stacked up) which then requires them to be turned on sequentially over time. The retinal persistence of the observer allows the selected colours to be recombined and the visible spectrum to be reproduced. Owing to the sequential power up, switching losses are generated. These are more significant the higher the capacitances to be switched owing to the fact that the layers of material forming the OLEDs are very thin. The superimposition of the sources also leads to losses of luminous intensity.
As an alternative, in U.S. Pat. No. 6,111,560, the implementation of rows of linear light sources was proposed, each one having a width such that several rows of the LCD switching array could act on the light produced by one illuminating line of the source. Lastly, in U.S. Pat. No. 5,796,509, the implementation of a lighting means was proposed that uses organic light-emitting diodes combined with a spatial optical modulator of the LCD type. Colour displays are described therein in which either the OLEDs produce white light and colour filters are employed or colour OLEDs are employed.
Other documents US2003/0030371 and WO99/66483 describe colour display devices equipped with this backlighting technology.
These various solutions still have limitations, especially relating to the accuracy of the optical reproduction or to the complexity of implementation and the present invention proposes to solve such problems, amongst others. Thus, a subject of the invention is a colour display device comprising, from rear to front towards an observer, a multicolour backlighting unit using organic light-emitting diodes (OLED) and an electro-optical array for the switching of the backlighting by pixels, the backlighting unit being a surface comprising a periodic pattern of a group of at least three adjacent illuminating lines of different base colours that are parallel to each other.